291
ctenostome, Vesicularia spinosa , Hincks ( 1873 , 1880 )
described embryo brooding accompanied by a change of
egg/embryo coloration and polypide degeneration. He
observed a “delicate envelope” [introvert] surrounding the
embryo, taking the view that the embryo develops inside the
zooid cavity. Later Calvet ( 1900 ) showed that brooding takes
place inside the introvert in this species. In Nolella stipata
(as Cylindroecium giganteum ), Hincks found three “ova” of
different sizes near the apex of the cystid interior, describing
their position as being “previous to escape” (see legend for
pl. 77, fi g. 4). Judging from their gradually increasing size,
these were brooded embryos, incorporated into the cystid
wall and nourished by it (indicative of matrotrophy). This
observation, again not understood, was later made by Prouho
( 1892 , pl. 24). While admitting the existence of cross-fertilization in some species, Hincks nevertheless believed that,
on the whole, self- fertilization prevailed in Bryozoa.
Following Joliet ( 1877a ), he thought that two ovaries could
be developed in succession within the same funiculus, confusing them with follicles of the same ovary developing
sequentially. He gave a general description of oogenesis and
mentioned that “frequently two ova [oocyte doublet] are produced, which are either matured in succession, or one of them
[leading oocyte] perfects its development at the expense of
the other, which is atrophied” [degeneration of the nurse cell]
( 1880 , p. xci). Remarkably, although he agreed with the opinion of Huxley ( 1856 ), Nitsche ( 1869 ) and Joliet ( 1877a ) about
the merely brooding function of the ovicell, Hincks continued
to insist that it could also produce eggs in some cases.
The most complete and precise descriptions of cheilostome reproduction at this time were made by Vigelius
( 1882 , 1884a , b ), who, in addition to observations of living
colonies, studied serial anatomical sections. Most latter
researchers employed this technique. Vigelius continued the
discussion about the origin of the ovary – whether it is
developed from the “endocyst” or from the “endosarc” (see
above). In Chartella membranaceotruncata (as Flustra
membranaceo-truncata ), he found developing ovaries on
the basal wall in distal parts of young zooids with latedeveloping polypide buds, and stated that they are formed
“from the internal surface of the endocyst” ( 1882 , p. 436),
since gonads were clearly isolated from the polypide, and
cell layers of the body wall and the ovary wall were continuous. According to his description, cells of the incipient
ovary are formed from the cells of the parietal layer,
“Parietalschicht” [epithelium of the body wall]. Furthermore,
they actively divide to form an ovary that initially consists
of a compact group of rounded cells of the same size. He
stressed their similarity to the early cells of the male gonad
and their common origin from the parietal layer, calling
them homologous. A similar suggestion was made earlier by
Joliet ( 1877a ). It should be mentioned here that the data of
Vigelius on the fl ustrid Chartella correspond to those of
Grant ( 1827 ), who observed the youngest eggs on the cystid
wall without a connection with the polypide in two other
fl ustrid species (see above).
Apart from the structure and development of the ovicell in
C. membranaceotruncata , Vigelius ( 1882 , 1884a , b ) gave
exhaustive and beautifully illustrated descriptions of oogenesis
and ovarian structure, starting from differentiation of 2–3 early
oocytes [in fact, oogonia] surrounded by smaller cells [ovary
wall] in the young ovary. Like Joliet ( 1877a ), Vigelius often
mentioned that eggs develop in pairs, and described growth of
the leading oocyte [judging from his illustrations, macrolecithal], surrounded by a “Dottermembran” [vitelline membrane]
and accompanied by changes in its cytoplasm during vitellogenesis and, fi nally, degeneration of the nurse cell [which
Vigelius considered as a struggle for existence between the
cells]. The structure of the ovary with its follicle (Vigelius was
one of the fi rst to use this term in bryozoan oogenesis) was
described as consisting of intensively pigmented, pear-shaped
and cylindrical lateral cells, adjoining the zooid wall, and paler,
fl attened cells on its opposite side ( 1884b ). Changes in ovary
shape and sometimes position were also mentioned. Vigelius
was sure that the cells of the ovary wall never transformed into
germinal cells, but that their number increased by division as
the follicle grew. He described ovulation, accompanied by a
gradual fl attening and eventual “resorption” of the follicle
cells, stages in the breakdown of the nucleus preceded by
shrinkage of the nuclear membrane, and removal of the mature
egg that occupies the larger part of the cystid cavity, towards
the distal transverse wall. He suggested that oviposition could
be performed by the activity of the parietal muscles of the zooidal frontal wall, contraction of which increases the pressure of
the perigastric fl uid, leading to the rupture of the ooecial vesicle
wall. The egg moved fi rst to the ooecial vesicle, later transferring through the hole in its ruptured wall to the incubation
cavity of the ovicell (Vigelius 1884a , b ). This scenario was
later adopted by Calvet ( 1900 ) and authors like Korschelt and
Heider ( 1910 ) and Gerwerzhagen ( 1913 ) (based on Calvet).
In Chartella Vigelius found male, female (more numerous) and occasionally hermaphrodite zooids in the same
colony. Because of the simultaneous presence of the three
variants of sexual zooids in the same colony, Vigelius supposed that female zooids could transform to hermaphrodite
and back to female depending on conditions. It was observed
that the gonads in the males appear later than ovaries in
female zooids in the colony. However, sperm mature at
approximately the same time as the eggs. The separation of
the sexes among zooids, the simultaneous maturation of their
gametes, and, in contrast, the generally different timing of
gamete maturation in hermaphrodite zooids [i.e. protogyny]
led him to support the suggestion of Joliet ( 1877a ) that crossfertilization should characterize this and most other species,
although it seems he meant intracolonial self- fertilization
[zooidal cross-fertilization within the same colony]. The
Appendices
ctenostome, Vesicularia spinosa , Hincks ( 1873 , 1880 )
described embryo brooding accompanied by a change of
egg/embryo coloration and polypide degeneration. He
observed a “delicate envelope” [introvert] surrounding the
embryo, taking the view that the embryo develops inside the
zooid cavity. Later Calvet ( 1900 ) showed that brooding takes
place inside the introvert in this species. In Nolella stipata
(as Cylindroecium giganteum ), Hincks found three “ova” of
different sizes near the apex of the cystid interior, describing
their position as being “previous to escape” (see legend for
pl. 77, fi g. 4). Judging from their gradually increasing size,
these were brooded embryos, incorporated into the cystid
wall and nourished by it (indicative of matrotrophy). This
observation, again not understood, was later made by Prouho
( 1892 , pl. 24). While admitting the existence of cross-fertilization in some species, Hincks nevertheless believed that,
on the whole, self- fertilization prevailed in Bryozoa.
Following Joliet ( 1877a ), he thought that two ovaries could
be developed in succession within the same funiculus, confusing them with follicles of the same ovary developing
sequentially. He gave a general description of oogenesis and
mentioned that “frequently two ova [oocyte doublet] are produced, which are either matured in succession, or one of them
[leading oocyte] perfects its development at the expense of
the other, which is atrophied” [degeneration of the nurse cell]
( 1880 , p. xci). Remarkably, although he agreed with the opinion of Huxley ( 1856 ), Nitsche ( 1869 ) and Joliet ( 1877a ) about
the merely brooding function of the ovicell, Hincks continued
to insist that it could also produce eggs in some cases.
The most complete and precise descriptions of cheilostome reproduction at this time were made by Vigelius
( 1882 , 1884a , b ), who, in addition to observations of living
colonies, studied serial anatomical sections. Most latter
researchers employed this technique. Vigelius continued the
discussion about the origin of the ovary – whether it is
developed from the “endocyst” or from the “endosarc” (see
above). In Chartella membranaceotruncata (as Flustra
membranaceo-truncata ), he found developing ovaries on
the basal wall in distal parts of young zooids with latedeveloping polypide buds, and stated that they are formed
“from the internal surface of the endocyst” ( 1882 , p. 436),
since gonads were clearly isolated from the polypide, and
cell layers of the body wall and the ovary wall were continuous. According to his description, cells of the incipient
ovary are formed from the cells of the parietal layer,
“Parietalschicht” [epithelium of the body wall]. Furthermore,
they actively divide to form an ovary that initially consists
of a compact group of rounded cells of the same size. He
stressed their similarity to the early cells of the male gonad
and their common origin from the parietal layer, calling
them homologous. A similar suggestion was made earlier by
Joliet ( 1877a ). It should be mentioned here that the data of
Vigelius on the fl ustrid Chartella correspond to those of
Grant ( 1827 ), who observed the youngest eggs on the cystid
wall without a connection with the polypide in two other
fl ustrid species (see above).
Apart from the structure and development of the ovicell in
C. membranaceotruncata , Vigelius ( 1882 , 1884a , b ) gave
exhaustive and beautifully illustrated descriptions of oogenesis
and ovarian structure, starting from differentiation of 2–3 early
oocytes [in fact, oogonia] surrounded by smaller cells [ovary
wall] in the young ovary. Like Joliet ( 1877a ), Vigelius often
mentioned that eggs develop in pairs, and described growth of
the leading oocyte [judging from his illustrations, macrolecithal], surrounded by a “Dottermembran” [vitelline membrane]
and accompanied by changes in its cytoplasm during vitellogenesis and, fi nally, degeneration of the nurse cell [which
Vigelius considered as a struggle for existence between the
cells]. The structure of the ovary with its follicle (Vigelius was
one of the fi rst to use this term in bryozoan oogenesis) was
described as consisting of intensively pigmented, pear-shaped
and cylindrical lateral cells, adjoining the zooid wall, and paler,
fl attened cells on its opposite side ( 1884b ). Changes in ovary
shape and sometimes position were also mentioned. Vigelius
was sure that the cells of the ovary wall never transformed into
germinal cells, but that their number increased by division as
the follicle grew. He described ovulation, accompanied by a
gradual fl attening and eventual “resorption” of the follicle
cells, stages in the breakdown of the nucleus preceded by
shrinkage of the nuclear membrane, and removal of the mature
egg that occupies the larger part of the cystid cavity, towards
the distal transverse wall. He suggested that oviposition could
be performed by the activity of the parietal muscles of the zooidal frontal wall, contraction of which increases the pressure of
the perigastric fl uid, leading to the rupture of the ooecial vesicle
wall. The egg moved fi rst to the ooecial vesicle, later transferring through the hole in its ruptured wall to the incubation
cavity of the ovicell (Vigelius 1884a , b ). This scenario was
later adopted by Calvet ( 1900 ) and authors like Korschelt and
Heider ( 1910 ) and Gerwerzhagen ( 1913 ) (based on Calvet).
In Chartella Vigelius found male, female (more numerous) and occasionally hermaphrodite zooids in the same
colony. Because of the simultaneous presence of the three
variants of sexual zooids in the same colony, Vigelius supposed that female zooids could transform to hermaphrodite
and back to female depending on conditions. It was observed
that the gonads in the males appear later than ovaries in
female zooids in the colony. However, sperm mature at
approximately the same time as the eggs. The separation of
the sexes among zooids, the simultaneous maturation of their
gametes, and, in contrast, the generally different timing of
gamete maturation in hermaphrodite zooids [i.e. protogyny]
led him to support the suggestion of Joliet ( 1877a ) that crossfertilization should characterize this and most other species,
although it seems he meant intracolonial self- fertilization
[zooidal cross-fertilization within the same colony]. The
Appendices